Coalescer apparatus for electrostatically resolving emulsions

ABSTRACT

A new apparatus is featured for electrostatically resolving solids-containing emulsions. The apparatus comprises a flexible electrode carrying electrolytes, therein in combination with a solids pump-off tube. Emulsions are resolved by passing current through the electrolyte at frequencies to or above 60 Hz.

FIELD OF THE INVENTION

This invention relates to coalescer apparatus for electrostaticallyresolving emulsions into their corresponding phases, and moreparticularly to electrostatic coalescer improvements in which certaindiffucult solids-containing emulsions can now be electrostaticallyresolved for the first time with the utilization of higher currentfrequencies and an improved solids pump-off tube.

BACKGROUND OF THE INVENTION

Heretofore, certain types of emulsions have been especially difficult toresolve by electrostatic means. These emulsions include: (1) high watercontent liquid membrane emulsions, (2) crude petroleum tanker andrefinery sludges, and (3) oil-continuous emulsions contaminated withelectrically conductive catalyst fines.

Another problem with electrostatic coalescer apparatuses is that theircurrent-carrying electrodes often develop pin-hole leaks in theelectrode insulation. These leaks result in arcing and general breakdownof the electrode's capability to resolve the emulsions. In addition,many electrodes are comprised of glass or other frangible materials,such that they are easily and often broken.

Emulsions with suspended fines and solids have shown particulardifficulty in being resolved, even when alternating current havingfrequencies in excess of 60 Hz are employed. Such a teaching is given inthe United States Patent to L. R. McCoy, U.S. Pat. No. 3,770,605;issued: Nov. 6, 1973.

Also, extreme resolution difficulties have been observed withelectrically conductive liquids, even despite the utilization offrequencies as high as 1,000 Hz. For purposes of definition,electrically conductive liquid emulsions are generally in the range offrom 0.1 to 1×10⁻¹⁰ or 1×10⁻¹² ohm⁻¹ cm⁻¹.

A teaching of this aforementioned problem is given in the United StatesPatent to L. R. McCoy and L. L. Prem, U.S. Pat. No. 3,839,176; issued:Oct. 1,1974.

The present invention seeks to resolve the problems set forth above, andin addition, desires to provide other advantages in coalescer methodsand apparatus.

The subject invention has successfully treated electrically conductiveand solids-containing emulsions at frequencies about 60 Hz. Theinvention has developed a new, solids pump-off tube in combination witha rugged electrode which makes possible improved emulsion-breakingtechniques, including dramatic increases in the throughput of thecoalescer system.

BRIEF SUMMARY OF THE INVENTION

The invention pertains to coalescer apparatus for electrostaticallyresolving emulsions into their corresponding phases. The coalescer isspecifically applicable to emulsions containing solids and withelectrically conductive emulsion liquids. Increase in the coalescenceapparatus throughput has been achieved. The coalescer apparatuscomprises:

a reaction vessel;

a means to introduce a solids-water-oil emulsion into said reactionvessel;

a current-carrying electrode disposed adjacent an interface of thephases of said emulsion;

a grounding electrode disposed in a water phase of said reaction vessel;

means to remove resolved phases of said emulsion from said reactionvessel; and

a solids pump-off tube disposed adjacent said interface and saidcurrent-carrying electrode, for removing solids from said reactionvessel.

It is an object of this invention to provide an improved coalescerapparatus for resolving solids-containing emulsions; and

it is another object of the invention to provide improved electrostaticresoltuion of emulsions, particularly solids-containing emulsions whichare especially difficult to resolve.

These and other objects of this invention will be better understood, andwill become more apparent with reference to the following detaileddescription considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a cylindrical coalescer apparatuscomprising an improved current-carrying electrode of this invention;

FIG. 2 is a schematic of a rectangular coalescer apparatus comprisingthe improved current-carrying electrode and solids pump-off tubecombination of this invention;

FIG. 3 is a cross-sectional view of the current-carrying electrode shownin FIGS. 1 and 2;

FIG. 4 is a schematic view of the inventive electrode of FIG. 3,featuring a spiral configuration for use in a vertically orientedcylindrical coalescer; and

FIG. 5 is a graph of the throughput (flow rate) verses the appliedvoltage for various frequencies of a coalescer system utilizing theinventive electrode of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 3, the current-carrying electrode 10 of this inventionis illustrated in a cross-sectional view. The electrode 10 comprises aninner support member 11, which is generally a rod or tube of conductivematerial such as a metal (preferably copper or stainless steel). Theinner support member 11 is concentrically surrounded by an outer tube 12of insulative plastic, such as Teflon®, polyethylene, nylon,polyvinyl-chloride, etc. The outer tube 12 is spaced from the innersupport member 11, which space is filled with an electrolyte 13.

The electrolyte can be any electrolyte which is compatible with theinner support material, i.e, copper or stainless steel. The electrolytecan be an acid, base, salt, molten salt, and a solid that becomeselectrically conductive at elevated temperature, such as beta alumina.

Referring to FIGS. 1 and 2, common embodiments of coalescer apparatusesare shown, which coalescer apparatuses comprise the inventive electrodeof FIG. 3. FIG. 1 depicts a cylindrical coalescer 20 orientedhorizontally. The coalescer has its current-carrying electrode 10connected to an alternating power source 21, which provides current tothe electrolyte of electrode 10. The electrode 10 is placed adjacent theinterface 22 between the aqueous phase 23 and the non-aqueous phase 24.The distance from the interface 22 may be critical, and thecurrent-carrying electrode 10 is usually placed about one inchtherefrom. Maximum electrode/interface spacing is approximately 3inches.

The emulsion can be stored in a reservoir 25, and pumped into reactionvessel 26 via pump 27.

The coalescer requires that at least one ground electrode 28 be placedin the aqueous phase 23. The coalescer of FIG. 1 also shows a groundelectrode 29 disposed in the non-aqueous phase 24. A pump 30 removes thenon-aqueous phase from vessel 26, while pump 31 removes the aqueousphase.

FIG. 2 illustrates a rectangular vessel 36 for a common coalescerapparatus. For purposes of brevity, like components will be given thesame designations throughout this text.

In the coalescer apparatus of FIG. 2, the emulsion is pumped fromreservoir 25 into vessel 36. A solids pump-off tube 35 having a designsimilar to a perforated distributor pipe is generally placedapproximately 5 mm from the interface 22 for a 3-phase solid-water-oilemulsion containing bi-wettable solids serves to pump away contaminantsolids from the interface 22. This tube makes possible the continuousoperation of the coalescer when treating solids-containing emulsions, asdepicted in Example 6, hereinafter.

In the coalescer apparatus of FIG. 2, several difficult emulsions wereresolved using the inventive methods and apparatus.

The minimum voltage for coalescence at a 1 in. separation should bearound 5 kV at 60 Hz to 1500 Hz. At a 2 in. separation the minimumvoltage was 7.5 kV at 400 Hz. The preferred voltage was greater than 10kV with values up to 20 kV considered suitable. Values in excess of 20kV may be employed at larger separations. The limiting factor on voltageis fixed by the dielectric properties of the insulating plastic tube 12.

Referring to FIG. 4, the electrode 10 is shown with a spiralconfiguration. Such a configuration is usefully employed in avertically-oriented cylindrical coalescer vessel.

All of the electrodes 10 are very durable. This is in contrast to theprior art glass electrodes or glass coated metals which are frangible.Plastic coated metals suffer from state-of-the-art limitations inbonding or adhesion characteristics between coating and substrate. Manyof these prior art electrodes develop pin-hole leaks, which results inarcing in the coalescer. The electrode affords ease of fabrication fromreadily available materials. Plastic tubing, e.g., Nylon, polyethylene,polyvinyl-chloride, Teflon®, etc., of thicknesses ranging from a fewhundreths of an inch up to around one-eighth of an inch arerepresentative materials useful for insulation. Tubing such as stainlesssteel or copper is suitable for the internal support.

Operation of the apparatus of FIG. 2 at frequencies of 400 Hz and aboveleads to significant size and cost reductions over conventional 60 Hzcoalescence.

The following examples illustrate the operation of the presentinvention. Selected feeds include high water content liquid membraneemulsions, crude petroleum and refinery sludges, and an oil continuousemulsion contaminated with conductive catalyst fines.

EXAMPLE 1

The set-up in FIG. 2 was used to coalesce a model liquid membraneemulsion consisting of a 2:1 ratio by volume of membrane (Isopar M) tointernal reference (distilled water containing 1 M H₂ SO₄) stabilizedwith 1 wt % ECA 4360 from Exxon Chemicals Co.

Performance data obtained with the apparatus given in FIG. 2 are givenin FIG. 5. The electrode 10 surface area was 183 cm². It was operated atan electrode spacing to ground of 1 in. Substantial increases insteady-state feed rate, Q, were noted with increasing frequency andapplied potential.

At 15 kV and 60 Hz, Q=70 ml/min while at the same potential and 1,000Hz, Q=295 ml/min. At 1,000 Hz, Q=80 ml/min for V=8.4 kV while Q=295ml/min at V=15 kV. The electrode 10 coating thickness of thepolyethylene was 0.125 in. Durability is the most prominent feature thathighlights this elecrode's usefulness.

Tables 1 and 2 below present a range of performance data for thepolyethylene electrode scaled up to a 1 GPM (8.75 b/d) feed (pilotlevel). The data show that both increased frequency and potential willlower the area required to process a fixed feed. Operation at 400 Hz andabove leads to a considerable reduction in electrode area. For example,for the polyethylene electrode 8.3 ft² of cross-sectional area isrequired for a 1 GPM feed at 60 Hz and 15 kV. Only 1.5 ft of electrodearea is required at 1,500 Hz while 2.9 ft² is needed at 400 Hz forsimilar 15 kV potentials. Significant reductions in electrode areaachieved at frequencies of 400 Hz and above permit correspondingreductions in coalescer size. Substantial cost savings should resultfrom size reductions.

                                      TABLE 1                                     __________________________________________________________________________    SCALE-UP REQUIREMENTS FOR INSULATED ELECTRODES                                AT 1 GPM FEED RATE                                                                          Total Surface                                                                        Cross-Sectional                                                        Area for                                                                             Area for                                                 f  Potential                                                                          Flow Rate                                                                           1 GPM Feed                                                                           1 GPM Feed                                               (Hz)                                                                             (KV) (ml/min)                                                                            (ft.sup.2)                                                                           (ft.sup.2)                                                                            Electrode Type                                   __________________________________________________________________________      60                                                                             15    70   10.6   8.3     Polyethylene Electrode                           1,500                                                                            15   388   1.9    1.5     Polyethylene Electrode                             400                                                                            15   200   3.7    2.9     Polyethylene Electrode                           __________________________________________________________________________     *Polyethylene electrode  183 cm surface area (142 cm crosssectional area)

                  TABLE 2                                                         ______________________________________                                        TANK SLUDGES BROKEN WITH                                                      INSULATED ELECTRODES                                                          Bayway Tank      Esso       Baton Rouge                                       542              Languedoc  Tank 284                                          ______________________________________                                        Electrode                                                                             Polyethylene Polyethylene                                                                             Polyethylene                                  Type    Teflon       Teflon     Teflon                                        Gradient                                                                              20            20         20                                           (kV/in)                                                                       Frequency                                                                             120,400      120        400                                           (Hz)                                                                          ______________________________________                                         *Tests at ambient and 150° F. for polyethylene and Teflon              electrodes.                                                                   **Required interfacial pumpoff of solids minimized at elevated                temperature.                                                             

Tests on similar model emulsions were carried out with uninsulated metalelectrodes. Violent arcing occurred in all but a few tests.

EXAMPLE 2

The apparatus in FIG. 2 containing the polyethylene electrode was usedto dehydrate a high water content crude tank sludge--Bayway crude oiltank 542 at ambient temperature. Analysis indicated a water content of24.8 wt. %, oil 73.5% inorganic solids 1.7%, specific conductivity7.27×10⁻⁷ ohm⁻¹ cm⁻¹, and dielectric constant 957. This sludge wasdiluted with Isopar "M" to make a 10:1 wt. ratio of Isopar/sludge. Testconditions were f=120 Hz and 400 Hz and 20 kV potential at an electrodeto interface distance of 1 in. Pump off of interfacial solids wascarried out whenever interfacial activity slowed down. Analysis of watercontent of the raffinate oil according to the Dean and Stark testindicated no measureable water.

This sludge could not be broken with an uninsulated metal electrode at a5 in. electrode separation distance for f=60, 120, 400, 1,000 and 1,500Hz at 10 kV to 20 kV. Moderate arcing was noted at this separationwithout any evidence of interfacial activity.

EXAMPLE 3

A low water content sludge (ESSO Languedoc) consisting of around 2.2% H₂O, 2.5% inorganic solids and 95% oil, specific conductivity 9.35×10⁻¹⁰ohm⁻¹ cm⁻¹, and dielectric constant 2.5 was tested similar to Example 2.The only difference being dilution with Isopar "M" in a 5:1 ratio.Analysis of water content according to the Dean and Stark test indicatedno water content in the raffinate oil.

As with Example 2, similar results occurred with uninsulated electrodes.Violent arcing occurred at 20 kV and f=120 Hz with uninsulatedelectrodes when a demulsifier Corexit 7651 (0.1 wt. %) was added, andthe electrode separation was reduced to around 2.5 in.

EXAMPLE 4

Another example of the present invention consisted of an oil continuousemulsion containing a high percentage of conductive catalyst fines(approximately 48%), 49% oil and around 3% water. The designation ofthis sludge was Baton Rouge Tank 284. The dielectric constant andspecific conductivity of this sludge were 2.6 and 7.29×10⁻¹⁰ ohm⁻¹ cm⁻¹,respectively. Dilution was in a 10:1 Isopar/sludge ratio. This feed wasrun continuously at 400 Hz and 20 kV with the polyethylene electrode 1in off the interface. The feed rate of 296 ml/min was balanced by an oilflow of 216 ml/min and a solids pump-off rate of 80 ml/min. Dean andStark type analysis indicated no water in the raffinate oil and thepump-off mixture.

EXAMPLE 5

Testing with a Teflon® insulated electrode (1/16 in. for tubing 12) wasextended to a cell temperature of 150° F. The preceeding three sludgesdid not exhibit interfacial problems even for solids layers as thick as5 mm. Pump off requirements are minimized therefore at hightemperatures. The Dean and Stark analysis for water for ESSO Languedoc,Bayway Tank 542, and Baton Rouge 284 indicated no water in the raffinateoil.

EXAMPLE 6

A continuous run was made with Tank 284, at a frequency of 200 Hz. Thecurrent-carrying electrode was 1" or 21/2 cm above the water interface.The pump-off tube was 2.3 cm from the water interface. The oil wasremoved at 216 ml/min. The solids were removed at 80 ml/min through thepump-off tube.

The present system is limited to the boiling point of water since anaqueous electrolyte serves as the internal contact. A direct extensionof this method would require addition of higher boiling point fluidswith high specific conductivities. Molten salts and conduiting solidselectrolytes are other exemplary extensions.

Having thus described the invention, what is desired to be protected byletters patent is presented in the following appended claims.

What is claimed is:
 1. A coalescer apparatus for resolving asolids-water-oil emulsion into its phases comprising,a reaction vessel;means to introduce a solids-water-oil emulsion into said reaction vesselto provide a water-oil interface in said vessel; a current carryingelectrode below said means for introducing said emulsion and disposed sothat under conditions of use said current-carrying electrode is adjacentsaid interface of the phases of said emulsion, said current-carryingelectrode having an inner support member for supporting an outerflexible plastic tube, said outer flexible plastic tube surrounding saidinner support member and being concentrically spaced therefrom so as toprovide a space therebetween, and an electrolyte disposed within saidspace between said support member and said plastic tube; a groundingelectrode disposed so that under conditions of use said groundingelectrode is in the water phase within said reaction vessel; means toremove resolved phases of said emulsion from said reaction vesselincluding a solids pump-off tube disposed so that under conditions ofuse said solids pump-off tube is between said current-carrying electrodeand said interface.
 2. The coalescer apparatus of claim 1, wherein saidsolids pump-off tube is disposed within approximately one inch of saidinterface.
 3. The coalescer apparatus of claim 1, wherein said solidspump-off tube is disposed substantially along the entire interface. 4.The coalescer apparatus of claim 1, wherein said reaction vessel isrectangular.
 5. The coalescer apparatus of claim 1, wherein said solidspump-off tube is designed similarly to a perforated distributor pipe.